This invention relates to a hydraulic assist device for a marine propulsion unit and more particularly to an improved device of this type.
It is well known to provide a hydraulic assist device that is interposed between a marine propulsion device such as an outboard motor or the outboard drive portion of an inboard/outboard drive and the transom of the associated watercraft. These devices serve a number of functions. Generally, the device is designed so as to permit the outboard drive to pop up when an underwater obstacle is struck and then permit the unit to return to its normal position. Preferably, the return should be to the previous trim adjusted position.
These devices normally include a cylinder that is connected to one of the watercraft and propulsion device and a piston that is contained within the cylinder and which is connected to the other of the watercraft and propulsion device. The piston divides the interior of the cylinder into a pair of fluid chambers and valves are provided in the piston so as to permit restricted flow from one chamber to the other when the underwater obstacle is struck and to provide return flow once the underwater obstacle is cleared.
In addition to these functions, it is also a common practice to provide a pressurized gas in one of the fluid chambers which acts to counterbalance at least the weight of the outboard drive so as to assist in manual tilting up of the outboard drive. In order to permit this manual tilting up without fluid resistance, a bypass line interconnects the two fluid chambers, and a valve is positioned in this bypass line that can be selectively opened and closed.
As should be readily apparent, these types of devices have a number of advantages, but also the prior art types of devices have some disadvantages, which can be best understood by reference to FIGS. 1-6. FIG. 1 is a schematic showing of the device FIGS. 2-6 are various views of the actual construction of the type utilized in the prior art. FIG. 2 2 is a side elevational view. FIG. 3 is a cross-sectional view taken along a plane extending perpendicular to the plane of FIG. 2. FIG. 4 is a cross-sectional view taken along the line 4--4 of FIG. 2. FIG. 5 is a cross-sectional view taken along the line 5--5 of FIG. 4 and shows the bypass valve in its normal condition. FIG. 6 is a cross-sectional view, in part similar to FIG. 5, and shows the bypass valve in its manual tilt-up position.
The prior art type of construction is indicated generally by the reference numeral 21. The manner in which it is adapted to be attached to the associated watercraft will be obvious to those skilled in the art, but FIG. 7, a view showing a preferred embodiment of the invention, may be referred to in order to determine how the device 21 is actually interposed between the watercraft transom and the outboard drive unit.
The device 21 is comprised of an outer cylinder assembly, indicated generally by the reference numeral 22. This cylinder assembly 22 has a trunion 23 formed at one end thereof to provide a pivotal connection to one of the transom and outboard drive. In the illustrated embodiments, this is to the outboard drive.
The cylinder assembly 22 is provided with an inner cylindrical bore 24 in which a piston, indicated generally by the reference numeral 25, is provided. The piston 25 divides the internal chamber of the cylinder 21 into an upper chamber 26 and a lower chamber 27. It should be noted that the upper chamber 26 is closed by a blind end of the cylinder assembly 22. The lower end of the chamber 24 is closed by a closure plug and gland assembly 28.
A piston rod 29 is affixed to the piston 25 and extends through the chamber 24 and beyond the enclosure and gland 28. A trunion 31 is fixed to the exposed end of the piston rod 29 to provide a pivotal connection to the remainder of the transom and outboard drive (the transom in this instance).
The lower chamber 24 is completely filled with a hydraulic fluid, and the upper chamber 26 is partially filled with the hydraulic fluid, as indicated by the legend A in the figure. The area in the chamber 26 above the fluid level A is filled with a compressed inert gas, such as nitrogen, in the area indicated at B. The chamber B is pressurized sufficiently so as to counterbalance some of the weight of the outboard drive for assisting in tilt-up action, as will become apparent.
Contained within the piston assembly 25 is a pressure responsive absorber valve, indicated generally by the reference numeral 32, and which is designed, in accordance with the attachment to the propulsion device and transom as aforedescribed, so as to permit flow from the chamber 27 to the chamber 26 when sufficient force is encountered on the outboard drive so as to cause it to pop up to clear the underwater obstacle that may have been struck. However, the pressure at which the valve 32 opens is set high enough so as to resist popping up of the outboard drive when operating in a reverse mode.
Once the underwater obstacle is cleared, the weight of the outboard drive causes fluid to be displaced from the chamber 26 back to the chamber 27 through a passage containing a relatively light let-down check valve 33.
It should be readily apparent that if an operator wished to tilt up the outboard drive through manual force, he would have to exert sufficient force so as to open the absorber valve 32. This obviously is more force than is desirable. Therefore, there is provided between the chambers 26 and 27 a tilt-up release valve, indicated generally by the reference numeral 34, and this is positioned in a bypass conduit that is indicated by the reference numeral 35. The structure is shown schematically in FIG. 1 and in actuality in FIGS. 2-6.
The passage 35 is comprised of a passage that is drilled axially through one end of the cylinder 22, and specifically the end adjacent the closure plug and gland 28. The outer end of this passage is closed, and the passage is cross drilled so as to communicate with the chamber 27. The upper end of this drilled passageway intersects a further passageway 36 that is drilled through the upper end of the cylinder 22 in proximity to the uppermost position of the piston 25. The outer end of the passageway 36 is closed by a plug 37.
This cross-drilled passageway 36 is offset from the vertically extending passageway, which is indicated by the reference numeral 38, and that passageway terminates in an area where a ball-type check valve 39 is positioned. The ball-type check valve 39 is normally urged to a closed position by means of a coil compression spring 41 so that the drilled portions 36 and 38 do not normally communicate with each other.
As may be seen in FIG. 1, the check valve formed by the ball 39 and spring 41 will permit passage of fluid from the chamber 26 to the chamber 27, but not in the reverse direction. The valve 39 is set to open at a relatively high pressure. In order to open the valve 39 manually, there is provided a manually rotatable actuator shaft, indicated generally by the reference numeral 42, which is journaled in the cylinder assembly 22 at a point offset from the drillings 38 and 36. A pin 43 is slidably supported in a further passageway 44 and engages a cam surface 45 formed on the actuator shaft 42. Upon rotation of the actuator shaft 42, the cam 45 will urge the pin 44 in a direction so as to unseat and open the ball check valve 39, as shown in FIG. 5. In this condition, the release valve 34 is opened, and this open passageway is shown schematically at 46 in FIG. 1.
As has been previously noted, when the release valve 34 is placed in its open position, the gas pressure in the chamber B will assist in the operator's lifting the propulsion unit without having to carry its full weight. However, this type of construction has several disadvantages, which will now be described.
First, it should be noted that the construction is such that in order to retain the outboard drive in its tilted-up position, some form of mechanical latch system must be provided. The reason for this is that even if the release valve 34 is moved to its closed position, as shown in FIG. 1, the weight of the outboard motor will cause fluid to be displaced from the chamber 26 through the light let-down valve 33 to the chamber 27, and the propulsion unit will return to a lowered position.
In addition, the trimmed-down condition of the outboard motor cannot be controlled by the hydraulic assembly as thus far described. This is because any downward forces, even when the release valve 34 is in its closed position, as shown in FIG. 1, cannot function to retain the propulsion unit in its upper position. This is because of the let-down valve 33.
Of course, the let-down valve 33 could be eliminated and then the trimmed-down position maintained by setting a high enough pressure on the valve 39 by using a strong spring 41. However, this is not totally satisfactory because the operator must manually overcome the action of the spring 41 to achieve a tilt up. Thus, it is typical with this type of construction to use a trim pin between the clamping bracket and swivel bracket of the outboard drive, and this must be adjusted manually each time the trim is to be changed. This is obviously not desirable.
Also, because of the type of valve employed and the fact that the pin 43 obscures part of the flow passage, the amount of pressure-assisted tilt-up operation is restricted, and this reduces the effect of the gas pressure assist.
In addition to these disadvantages, the ball valve 39 must also be forced against hydraulic pressure to release it, as well as the spring pressure, and this makes even manual release of the valve difficult.
It is, therefore, a principal object of this invention to provide an improved hydraulic assist device for a marine propulsion unit.
It is a further object of this invention to provide a hydraulic assist device for a marine propulsion unit that will be capable of setting the trim adjusted position of the marine propulsion unit and which will ensure that the unit returns to that position once it has popped up after striking an underwater object.
It is a further object of this invention to provide an improved release valve assembly for a hydraulic assist device for a marine propulsion unit.